Air conditioning



M r h 1 40'.- G. v. WOQDUNG 2.194.041

AIR CONDITIONING Original Filed April 22, 1932 Sheets-Sheet 1 PSYCHROMETRIC CHHRT WDTH r EFFECTIVE TEMPERHTURE LINES FOR STILL m2 coumnoms PERSONS NORMHLLY CLOTHED 1 AND SLIGHTLY ACTIVE z, 4 A.S.H.V.E.

i200 Research Laboratory a U.S. Bureau of Mmes & Piltsburgh, Pa.

E as 3O b0 /00 //0 L20 Dry bulb Tempemtu e 280 H ME IC CHHET WIT EFFECTIVE TEMPERBTUEE LINES kZ40 me VELOCITY OF 300 FTPERMI PERSONS NOBMHLLY CLOTHED AND SLIGHTLY FICTIVE g A.5. H. V. E. 200 rch Laboratory US Bureau of Hmes g 'uzsbur-gh. Fa. I :weo +1 i 13/20 7;,

h S U k w 40 so 70 80 90 I00 1/ Dry bulb Temperature INVENTOR.

HIS ATTORNEYS.

Mam]! 19, G. v. wooouue 2,194,041

' AIR counrrxonme Origipal Filed April 22, 1932 Sheets-Sheet 2 (929: 3 lPe/azive Humidity Scale L M090 aa 70 60 50 4a 3o zv/V Dlffereniial Terqperature Sea-Le.

Dry Bul b-Wet Bulb Dry Bulb Temperature Scale Wei Bulb Temperature Scale Effective Tmperaiure Scale 05/0 za oarD liu Q 5 7 4 L, g g //0 m \I Q a Q 7 10.9

s D O Q Q g Q; Q: i S g g N s E 0 /0 2o 4o 3 Differential Emperazures E )1 i 2 J g 6 mg 200 I00 L Q U) Q 7 300 G 2 Radial fllsiances= Lmear Umfs as o 30 X mar/ed ff Amount to be subimeted fro/n fig/B g 40o scale E F kwperatuzes to equal Effective,

Temperatures 500 INVENTOYR.

BY W MM 7124:

ms ATTORNEYS.

March 19, 1940. s. v. WOODLING 2,194,041

AIR comm'ronnm Original Filed April 22, 1932 5 Sheets-Sheet 3 l WN MN Wet Bulb f 50! E 5 2 Q 5o8 5 5/ 4 07 X 1 Dry Bulb 7506- E; :1 500 g Anemometer v jhaft 547 3's ATTORNEYS.

March 19, 1940. v, WQQDLING 2,194,041

' AIR CONDITIONING Original Filed April 22, 1932 5 Sheets-Sheet 4 flame of [{q/rt ,eelaflue llumzdliy Graph -Hem her I 520 I as I ah 4:0 5'0 6'0 70:54:79?!

Relative Ham 1' c1 z'iy as. m. a A

Values for the lllus ira ted P051 tic/7s 1. Dry Bulb fizmperaure 90 2. Wet Bulb Temperaiure 72 3. fliffercniial Em erazuee /8 HIS ATTORNEYS Patented Mar. 19, 1940 UNITED STATES PATENT AIR CONDITIONING George V. Woodling, Cleveland, Ohio, assignor to General Motors Corporation, a corporation of Delaware Application December 3,

1932, Serial No. 645,570,

9 Claims.

My invention relates, in general, to air conditioning, and more particularly to means for measuring and regulating the condition of the air to give the maximum degree of comfort.

This application is a division of my pendin application for Letters Patent, Serial No. 645,570, filed December 3, 1932 which issued as Patent No. 2,166,697; July 18, 1939, which is a division of my application for Letters Patent, Serial No. 606,837, filed April 22, 1932, which issued as Patent No. 2,139,295, December 6, 1938.

An object of my invention is to provide for measuring'and regulating the relative humidity and'the eifective temperature of air to give the maximum degree of comfort.

Another object of my invention is'to give a measurement that is a true index of a persons feeling of comfort or discomfort in all combinations'of the dry bulb temperature, the relative humidity and the air velocity.

A further object of my invention is to translate three movements into a single resultant movement.

A'still further object of my invention is the provision of a psychrometric device that measures the eifective temperature in all combinations of the dry bulb temperature, the relative humidity, and the air velocity. 1

Another object of my invention is the provision of a psychrometric device that is responsive to the dry and wet bulb temperatures for measuring the relative humidity.

It is also an object of my invention to provide for regulating the effective temperature of the air in a building, or in am enclosure, in accordance with the efi'ective temperature of the air on the outside of the building or the enclosure.

It is a further object of my invention to cause the movements of the psychrometric device to vary the amount of light falling upon .a photoelectric cell forcontrolling the air conditioning equipment, the heating apparatus, or the humidifying equipment.

A still further object of my invention is the combination of a psychrometric device and photo-electric cells, together with suitable amplifying circuits, for controlling the air conditioning equipment, the heating apparatus, or the humidifying equipment to give the maximum degree of comfort. 7

Another object of my invention is to provide for so regulating the drybulb temperature that, for any change in the relative humidity or the air velocity which results in a change in the efiectivej temperature, a correction is made in the dry-bulb temperature to ofi-set the said change in the eiiective temperature caused by the change in the relative humidity or the air velocity.

Other objects and a iuller understanding of my invention may be had by referring to the following descriptions, taken in connection with the accompanying'drawings, in which:

Fig. 1 is a psychrometricchart with effective temperature lines for still air conditions, persons normally clothed and slightly active,

Fig. 2 is a psychrometric chart with efiective temperature lines for an air velocity of 300 feet per minute, persons normally clothed and slightly active.

Fig. 3 is the graphical representation of a method for determining the relative humidity from the dry-bulb and wet-bulb temperature,

Fig. 4 is the graphical representation of a meth- 0d for'determining the effective temperature for all combinations of dry-bulb temperatures,.wetbulb temperatures, and air velocities,

Fig. 5 is a graph showing the relationship between the linear. displacement plotted against the numerical values, as marked oil on the line CD of Fig. 4, a

Fig. 6 is a graph showing the relationship between the linear displacement plotted against the numerical values, as marked off on the line EF of Fig. 4,

Fig. 7 is a plan view of a psychrometric device that measures both the relative humidity for all combinations ofdryand wet-bulb temperatures, and the effective temperature for all combin a-' tions of the dryand wet-bulb temperatures, together with the air velocities,

Fig. 8 is a rear elevational view of metric device, shown in Fig. 7,

Fig. 9 is aview taken along the lines 11-?) of Fig. 7, part of the elements being omitted to clarify the view, as well as to explain the re1ative angular displacements of the various parts,

Fig. 10 is a front elevational view of the psychrometric device shown in Fig. '7, and illustrates indicating hands for the dry-bulb temperature, the wet-bulb temperatures, the efiective temperature, and the relative humidity, together with graph-members based upon the effective temperature and the relative humidity,

Fig. 11 is adiagrammatic view of two fundamental circuits that may be associated with two psychrometrlc devices for regulating the' effective temperature of the air inside of a building in accordance with the efiective temperature of the air surrounding the building,

the psychro- Fig. 12 is a graph, together with a chart upon which it is based, showing the desirable inside effective temperatures as compared to the outside effective temperatures,

Fig. 13 is a fundamental circuit that may be associated with the psychrometric device for regulating the relative humidity of a building or enclosure at any predetermined selected value,

Fig. 14 is a modified form of the circuit shown in Fig. 13, and employs grid-controlled glowdischarge tubes for operating the air conditioning equipment,

Fig. 15 is a fragmentary showing of a control system wherein the electro-magnets that operate the air conditioning equipment may be operated by a control circuit employing grid-controlled glow-discharge tubes, such as the circuit shown in Fig. l4, and

Fig. 16 is a diagrammatic view showing conventional air conditioning apparatus which may be controlled by the control system shown in Fig. 11.

The effective temperature is an experimentally determined scale, and therefore represents the true index of a persons feeling of warmth in all combinations of temperature, humidity, and air motion.

The temperature sensations of the human body depend not only upon the temperature of the surrounding air as registered by a dry-bulb thermometer, but also upon the temperature as indicated by the wet-bulb thermometer, together with the air motion. Human comfort or discomfort, as regards feeling of warmth, depends largely upon the body temperature, and, therefore, upon the relation between the rate of production and dissipation of heat.

By the process of metabolism heat is constantly generated within the body, which heat must be eliminated from the surface of the body and from the respiratory tract by radiation, convection and evaporation. Hence, to maintain a constant body temperature the heat loss must equal the heat produced. It is, therefore, apparent that any reduction in the elimination of heat from the body must result in a rise in temperature and a corresponding feeling of discomfort. As the temperature of the air and surrounding objects rise, the loss of heat by convection and radiation decreases. When the air temperature reaches that of the body, the loss by radiation and convection ceases. Finally, as the air temperature exceeds that of the body, heat is transferred from the air to the body. As the temperature of the air rises and heat loss by radiation and convection decreases, the body endeavors to maintain temperature equilibrium by making available more perspiration, thus resulting in a greater heat loss by evaporation.

From the foregoing, one notes that there must necessarily exist certain combinations of air tem peratures, air humidities and air motion, which produce the same total heat loss from a person by radiation, convection, and evaporation which produce the same feeling of comfort or discomfort upon the person notwithstanding variations in one or more components of said combinations.

The combination of temperature, humidity and air movement which produces the same feeling of warmth are called thermo-equivalent conditions or effective temperature lines. Elaborate experiments show that this newly developed skill of thermal equivalent conditions not only indicates the sensation of warmth, but also determines the physiologic: l effects on the body induced by heat and cold. For this reason, the thermo-equivalent condition is generally referred to as the effective temperature scale or index.

Effective temperature is an experimentally determined scale which unlike the dry-bulb and wet-bulb scales is a true measure or index of a persons feeling of warmth in all combinations of temperature, humidity, and air movements. In other words, for any one given effective temperature a person feels the same degree of warmth or coldness regardless of the dry-bulb temperature, the wet-bulb temperature, and velocity of the air required to produce that particular effective temperature.

With reference to the two psychrometric charts of Figs. 1 and 2, the dry bulb temperature is plotted as abscissae and the grains of moisture per pound of dry air as ordinates. The maximum moisture which the air can hold at various temperatures gives the saturation, or 100 percent relative humidity curve. Relative humidities between zero and 100 percent are given by a series of curved lines similar to the saturation curve. The wet-bulb temperatures for all atmospheric conditions are given by a series of nearly parallel oblique lines. Effective temperature is given by a series of oblique but not parallel lines which approach being parallel to the wet-bulb lines at high temperatures. In the psychrometric chart of Fig. l, which is for still air, the effective temperature line is vertical and coincides with the dry-bulb temperature line at 46. In Fig. 2, which is for air moving at the rate of 300 feet per minute, the effective temperature line is vertical and coincides with the dry-bulb temperature line at 56. Although not shown, for air velocities of 100 and 500 feet per minute the effective temperature lines and the dry-bulb temperature lines coincide respectively at 51 and 59.

For dry-bulb temperatures below these respective values, an increase in humidity produces a cooler sensation, instead of a warmer sensation as is produced for dry-bulb temperatures above these values. The values may be called the dividing lines at which humidity has no effect upon the comfort of the body.

The psychrometric chart of Fig. 2 for moving air, differs from the chart of Fig. 1 for still air only in that the effective temperature lines for any particular degree do not intersect the drybulb, and wet-bulb temperature lines at the same degree on the saturation or 100 percent relative humidity curve, but are removed to the right so that the effective temperature for any dry and wet bulb temperature is lower for moving air than it is for still air. This difference between the effective temperature for still air and for moving air, of any velocity, is the cooling resulting from that velocity.

Referring to the psychrometric chart in Fig. 1, a dry-bulb temperature of 70 and a wet-bulb temperature of 54 produces an effective temperature of 65". This is for still air. Referring to Fig. 2, which is for air moving at the rate of 300 feet per minute, the same dry and wet bulb temperatures produces an effective temperature of 60, or a reduction of 5 resulting from a change in air velocity.

'For winter-time conditions in relatively cold climates, and for persons 'normally clothed and slightly active, extensive tests show that the comfort zone ranges from an effective temperature of 62 F. to an effective temperature of 69 F. That particular effective temperature at which a maximum number of people feel comfortable is called While at rest, 9'7 percent ofcomfort line or optimum effective temperature.

However, persons working at various rates are most comfortable at efiective temperatures below 64 F. The foregoing discussion respecting the effective-temperature is merely arbrief restatement of the subject matter published in the Transactions of the American Society of Heating and Ventilating Engineers from 1923 to the present date by F. C. Haughten and C. P. Yaglou.

Since one of the purposes of the psychrometric device is to measure the effective temperature, it follows that its functioning must be based upon a useful and practical relationship that combines the dry-bulb temperature, the relative humidity, and the air motion. From a study of the psychrometric charts of Figs. 1 and 2, together with other psychrometric charts (not shown), I find that by reorganizing the foregoing values upon a different basis, a'useful and practical relation results. Such a relationship is shown in Fig. 4. In this relationship, however, the relative humidlty is not considered directly, but by its derived value, as determined by the dry-bulb and wet-bulb readings.

In Fig. 4, the dry-bulb temperature is scaled off on the line OY; the amount to be substracted from the dry bulb to equal the effective temperature on the line OK; the difference between the dry-bulb and the wet-bulb temperatures on the line CD; and the air velocities on the line EF.

The air velocity line, EF, is determined as follows: With reference to the psychrometric chart of Fig. 1, which is for still air, one observes that, at a dry-bulb temperature of 46, the amount to be substracted from the dry-bulb temperature to equal the effective temperature is zero. This establishes the zero point on the line EF. Simidarly, with referenceto the psychrometric chart of Fig. 2, which is for an air velocity of 300 feet per minute, one observes that, at a dry-bulb temperature of 56, the amount to be substracted from the dry-bulb temperature to equal the effective temperature is 10. This establishes the point 300 on the line EF. The points for air velocities of 100, 200, 400 and 500 may be established in a similar manner.

The line CD is likewise empirically established by first plotting a family of lines which have for their base the line EF and whichconverge at a dry-bulb temperature of 120 F. The values for plotting the family of lines are obtained from the psychrometric charts of Figs. 1 and 2, to-

gether with other similar charts (not shown). For instance, the line G, interconnecting the zero point on the line EF and the point 5 on the line CD is determined by establishing a series of points, the values of which being obtained from the psychrometric chart of Fig. 1, and drawing a line through the said points. With reference to Fig. 1, which is for still air, we observe that, at a. dry-bulb temperature of F. and a wet bulb temperature of 70 F., (a difference of 5), the effective temperature is 72.7 F. This means that, at a dry-bulb temperature of 75 F. and with a difference of 5 between the dry-bulb and the wet-bulb temperatures, the amount to be substracted from the dry-bulb temperature to equal the corresponding effective temperature, is 2.3. Therefore, with reference to Fig. 4, a dry-bulb temperature of 75 F., as measured on the line CY, and a value of 2.3", as.measposes, be considered straight.

ured on the line OX, established a point h" for the line G. For the point i, on the line G, we

observe from Fig. 1 that the amount to be substracted from a dry-bulb temperature of 100 F. (with a wet-bulb temperature of F.) to equal the corresponding effective temperature, is 4. Similarly, for the point 5, being the point where the line G intersects the line CD, we observe ,from Fig. 1 that the amount to be substracted -on the line EF, and the points 10, 20 and 30 on the line CD may be established in the same manner as the line G was established, except that the differences between the dry-bulb temperatures and the wet-bulb temperatures are 10, 20 and 30 respectively.

The family of lines interconnecting the point 300 on the line EF and the points 5, 10 and 20 on the line CD may also be established in a similar manner, except that the values for establishing these lines are taken from the psychrometric chart in Fig. 2, which is for an air velocity of 300 feet per minute. The values for determining the family of lines interconnecting the points and 500 on the line EF and the points 5, 10 and 20 on the line CD are taken from psychrometric charts (not shown) for air velocities of 100 and 500' feet per minute, respectively. As will be observed, all of these lines are substantially straight, except those for the higher air velocities, and they may, for all practical pur- While I have drawn the foregoing family of lines to explain the method as to how they are established, it is readily apparent that an infinite number of such lines may be drawn. From the reorganized psychrometric chart of Fig. 4, one observes that the family of lines converge at F., thus indicating that at this high temperature the air velocity has no cooling effect upon the body. Therefore, when the chart in Fig. 4 is once established, we can obtain from it the amount to be substracted from the dry-bulb temperature to equal the corresponding effective temperature for all possible combinations of dry-bulb temperature, wet-bulb temperatures and air velocities. As will appear later, that part of the psychrometric device for measuring the effective temperature is based upon the chart of Fig. 4. However, before describing the structural features of the psychrometric device, I will explain the basis for directly determining the relative humidity from the dry-bulb and wet-bulb temperature readings.

With reference to the chart in Fig. 3, the drybulb temperature readings are scaled off on the arcuate line JK; the difference between'the drybulb and the wet-bulb temperatures on the arcuate line LM; and the relative humidity on the straight horizontal line LN. The angular position of the arcuate line LM relative to the arcuate line JK is determined by making the zero or starting point of the line LM and the drybulb temperature reading of 60 on the line JK lie on the same radius; namely, the line OPL. The radial position of the arcuate line JK relative to the arcuate line LM is such that the distance OP equals two-thirds of the radial distance OL. However, any other ratio may be employed so long as the proper considerations of all the factors effecting the ratio are taken into account. As illustrated, the dry-bulb temperature readings, as marked off on the arcuate line JK, range from 46 to 120 F., and the differential readings, as marked off on the arcuate line LM, range from to 35. These temperature readings correspond to those shown in Fig. 4. and are more than adequate to accommodate any and all possible heating and air conditioning requirements. The relative arcuate lengths of the dry-bulb temperature scale JK and the differential scale LM may bear substantially the same proportion as shown. However, should it be desirable to reduce the length of the relative humidity scale LN, this may be done by reducing the arcuate length of the differential scale LM relative to the arcuate length of the dry-bulb temperature scale JK. Both the position and the readings, as marked off on the relative humidity line LN, are established empirically by drawing intersecting lines through the dry-bulb temperature scale JK and the differential scale LM. Referring again to the psychrometric chart of Fig. 1, we observe that a dry-bulb temperature of 70 and a wet-bulb temperature of 59 (a difference of 1 give a relative humidity of 50 percent, and that a dry-bulb temperature of 100 and a wet-bulb temperature of 84 (a difference of 16) likewise give a relative humidity of 50 percent. Hence, the intersection of a line drawn through 70 on the scale JK and 11 on the scale LM with a line drawn through 100 on the line JK and 16 on the scale LM determines'the point for 50 percent relative humidity. Similarly, the intersection of a line drawn through a 70 on the scale JK and 14 on the scale LM with a line drawn through 100 on the scale JK and 20.5 on the scale LM determines the point for 40 percent relative humidity. As illustrated, other points for the relative humidity line LN may be determined in a similar manner. I find that, by plotting the chart shown in Fig. 3 on a large scale the working range of the relative humidity scale LN is very accurate. However, there is a slight percentage of error at the extreme ends of the scale.

That part of the psychrometric device for measuring the relative humidity is based upon the chart in Fig. 4. As far as it is possible to do so, the two parts will be described separately, even though structurally they are mutually dependent. I will describe the part concerning the relative humidity first.

With particular reference to Figs. 7, 8, 9 and 10, the reference characters 500 and 50| represent two rotatable shafts, the rotation of which are, respectively, responsive to the dryand. wet-bulb temperatures. Several methods, well known in the art, are available for operating the dry and wet temperature shafts, but, since this constitutes no part of my invention, I have omitted making a showing of such a means. Generally, such a means may comprise a tube containing a thermo-expansive fluid connected to a Bourdon tube helix which expands and unwinds in a well known manner to rotate the said shafts. For the dry-bulb temperature shaft 500, the tube that contains the thermo-expansive fluid is exposed to the ordinary atmosphere and for the wet-bulb temperature shaft 50!, the tube may be either surrounded with a wick dipped into a tank of water or any other means to eflect an evaporation. Also, as a modification, the dryand wet-bulb shafts 500 and 50| may be remotely controlled by an electrical means that is responsive to a dryand a wet-bulb thermometer.

As illustrated, the dryand wet-bulb temperature shafts are rotatively mounted in brackets 502 which are supported by a base member 503. Through a transmission of the planetary type, the two shafts are arranged to operate a drybulb temperature hand 505 and a differential temperature hand 506. As shown in Fig. 10, the dry-bulb temperature scale JK, the differential temperature scale LM, and the relative humidity scale LN provided upon the face 509 of the psychrometric device are constructed upon the same basis as the chart shown in Fig. 3. The effective temperature hand is represented by the reference character 50! and the wet-bulb temperature hand by 508. Their values are read off on the dry-bulb temperature scale JK The dry-bulb temperature shaft 500 extends through the various parts of the psychrometric device and the dry-bulb temperature hand 505 is connected upon the outer or right-hand end thereof. Surrounding the dry-bulb temperature shaft 500 is a hollow or tubular shaft 5|0, and the differential temperature hand 506 is connected to the outer or right-hand end thereof and the rear or left-hand end thereof is con nected to the differential transmission. Inasmuch as the linear arcuate unit for the differential scale LM is larger than the corresponding arcuate linear unit for the dry-bulb temperature scale JK, the left-hand end of the tubular shaft 5|0 is connected to the sun gear 5|2 and the dry-bulb temperature shaft 500 is connected through the usual spider to the planetary gears 5|3 of the differential transmission. The orbit gear 5M of the transmission is driven by the wet bulb temperature shaft 50| through a gear wheel 5|5. In this manner, the difference in angular displacement of the dry-and wet-bulb temperature shafts is transmitted through the sun gear 5|2 and hence the tubular shaft 5| 0 to the differential hand 506. The gear wheels of the planetary transmission are so proportioned that, for any reading of the dryand thewet-bulb temperature hands 505 and 508, as marked off on the scale JK, the differential hand 506 indicates a value, as marked off on the differential scale LM, that is the difference between the dryand wet-bulb temperature readings.

As illustrated, the relative humidity scale LN may be horizontally supported upon the face 509 by suitable pins 5! 6 or their equivalents. The lower edge of the relative humidity scale is provided with a longitudinal slot in which a pin 5|! is disposed to be slidably mounted. Interconnecting the pin 5!! and the outer ends of the dry-bulb temperature hand 505 and the differential temperature hand 506 is a slotted arm 5|8. Hence, as the dry-bulb temperature hand 505 and the differential temperature hand assumes different relative positions, the upper end of the slotted arm 5!!! constrains the pin 5|! to move along the longitudinal slot of the relative humidity scale LN. The position of the pin 5| 8 determines the relative humidity reading for the corresponding readings of the dryand wet-bulb temperatures.

In the position as shown, the dry-bulb temperature hand 505 indicates a temperature of 90 upon the scale JK and the differential temperature of 18. For this position of the dry-bulb temperature hand 505 and the differential hand 506, the corresponding relative humidity reading narrow slit H2.

is 40 percent. This particular setting of the hands is also indicated on the chart shown in Fig. 3. The heavy line 505 represents the position of the dry-bulb temperature hand 505; the heavy line 506 indicates the position of the differential hand 5% and the heavy line m indicates the slotted arm 5 l 8. As is readily apparent, my psychrometric device provides for measuring the relative humidity for any and all possible combinations of dry-bulb and wet-bulb tem-- peratures.

For the purpose of regulating the humidifying equipment of an air conditioning system, I provide a relative humidity graph-member 520 and a light projector H2 (see Figs. 10 and 13) for varying the amount of light falling upon a photoelectric cell lit of an amplifying circuit, which, in turn, actuatesa pole changer relay 525 for controlling the polarity of the current delivered to the humidifying equipment. The amplifying circuit and the light projector H2 for accomplishing this result are shown in Fig. 13.

'Iwowell'lrnown methods are available for varying the amount of light that passes through the light transmitting portion N4 of the graph-member 5213. One may be termed the linear method, and the other the area method. .With reference to the light projector N2, the linear method may be described'as follows: Thelight projector H2 comprises, in general, a cylindrical housing H9 in which are disposed, at the left end. two condensing lenses I20 and, at the right end, two objective lenses HI, and, in the middle, a transversely disposed member having a vertical By means of the condensing lenses H0 and the objective lenses 52!, and the slit I22, the light from the concentrated filament of the lamp Ill is formed into a plane of light. The intensity of this plane of light may be suitably varied by the adjustable resistor ld5 that is connected in circuit relation with the source of electrical energy I42.

As shown, this plane of light is directed perpendicularly to the plane'of the transversely disposed relative humidity graph-member 520. By reason of the demagnifying effect of the lenses the width of the plane of light at its focal point, being the point at which it passes through the light transmitting portion M41, is several times smaller than the width of the slit I22. The breadth or the height of the Plane of light is slightly greater than the maximumheight of the light transmitting portion H4. Therefore, the

quantity of light falling upon the photo-electric cell H0 is determined by the amount that the graph-member 520 is transversely moved relativey to the plane of light, or, in other words. by the height of the ordinate of the light transmitt ng portion H4 The graph-member 520, may be constructed either of a thin sheet of opaque material or of a photographic film. When the graph-member 526 is constructed of a thin sheet of opaque material, the light transmitting portion ll t takes the form of an aperture, but when a photographic film is used. the light transmitting portion H6 is transparent while the surrounding portion is dark. In the case of a photographic film it is essential that the degree of transparency be uniform throughout the light transmitting portion H4. By utilizing a photographic film, the graph-member may be plotted on an enlarged scale and reduced to a size. applicable for the photo-electric cell by taking a reduced photograph of the enlarged, graph-member.

This

of making graph-members. As is apparent, the maximum height of the light transmitting portions of the graph-members must not exceed the illumination boundaries of a photo-electric cell.

The relative humidity graph-member 520 is connected to the upper end of the slotted arm 538 and may be slidably mounted in any suitable manner with reference to the light source Ill makes a very accurate and convenient methodand the photo-electric cell. ill] of the amplifying i I circuit of Fig. 13. With reference to the rela tive humidity graph-member 520, the vertical dotted line represents the plane of light. In order to make the showing of the hands of the psychrometric device as clear as possible, I have omitted the relative humidity graph-member 520 in Fig. 7. The base of the light transmitting portion of the-relative humidity graph-member 520 is the same length as the relative humidity scale LN and to every relative humidity 'value, as marked off on the base of the=light transmitting portion there corresponds an ordinate of the same value. Therefore, the amount of light falling upon the photo-electric cell H0 is directly proportional to the readings of the relative humidity.

The photo-electric cell H0 is a light sensitive device which, when connected to a circuit of the proper potential and when illuminated from a suitable source, passes a very small amount of current of the order of micro-amperes. The photo-electric cell llll comprises, generally, an anode l I! and a cathode I I8 sealed within either an evacuated space or within a space filled with a gas at a very low pressure. The cathode H8 is constructed of a material that has the property of liberating electrons when illuminated. By impressing a potential of the proper polarity and magnitude between the anode H1 and the oathode Il8, the liberated electrons move toward the anode H1, thus effecting a passage of current in response to the light falling upon the cathode H8. Throughout the usual range of illumination, the current passed by a photo-electric cell is directly proportional to the illumination.

i As is well known in the art, the feeble current that is passed by a photo-electric cell may, by means of either thermionic amplifiers or by gridcontrolled glow-discharge tubes, be eifectively amplified to operate electrical meters and sturdy relays. Each type of amplification has certain distinct advantages over the other.

Under correct and proper operating conditions, the out-put of a thermionic amplifier is directly proportional to the light falling upon the photoelectric cell, whereas this is not exactly true with grid-controlled glow-discharge tubes. However, with the proper circuits, a fair degree of proportionality can be obtained by utilizing grid-controlled glow-discharge tubes. Byreason of the high degree of proportionality, the combination of the photo-electric cell and the thermionic amplifiers, provides agood light meter and may, therefore, be suitably adapted to give calibrated indications and to operate pilot relays.

Although there are many amplifying circuits utilizing thermionic amplifiers with either direct in alternating current, or with one or more stages of amplification, I have preferably illustrated in Fig. 13, a simple direct current thermionic amplifying circuit having only one stage of amplification. However, it is to be understood that I do not intend to limit my invention to the illustrated embodiment.

The illustrated amplifying circuit of Fig. 13

comprises, in general, the thermionic. tube II5 having a filament I3I, a grid I32, and a plate I33, a grid resistor I40, a grid potentiometer Ill for biasing the potential of the grid I32, relative to 4 the filament I3I, a filament battery I34, aplate battery I35, and a grid potentiometer battery I38. The plate battery I35 and the grid potentiometer battery I35 are connected in series circuit relation so that the sum of their voltages, except as modified by the grid potentiometer III, is impressed across the anode H1 and the cathode II8 of the photo-electric cell IIII.

In operation, when no light is falling upon the photo-electric cell IIIi, it passes no current, with the result that the grid I32 of the thermionic tube I I5 is sufliciently negatively charged with respect to the filament I3I, as determined by the setting of the grid potentiometer Ill, that the value of the impedance between the plate I33 and -the filament I 3I is sufilciently high that very little, if any, plate current flows through the thermionic tube I,I5. However, when the photo-electric cell H0 is illuminated. it passes a current for decreasing the impedance of the thermionic tube H5. The current passed by the photoelectric cell IIO flows from the positive terminal of the battery I35 through the winding of the relay 525, the relative humidity recording meter 526, conductors I5I and I52, the anode land the cathode II8 of the photo-electric cell, a conductor I 53, the grid resistor I45, the grid potentiometer HI, and to the batteries I35 and I35. The current flowing through the photo-electric cell IIO causes a voltage drop over the grid resistor I40 in such direction as to cause the grid I32 to become less negatively charged with respect to the filament I3I, with the result that the impedance of the thermionic tube 5 decreases. A decrease in the impedance of the thermionic tube I I5 allows a plate current to flow from the positive terminal of the battery I35.

through the winding of the relay 525, the recording meter 526, the plate I33 and the filament I3I of the thermionic tube, and to the negative terminal of the battery I35.

The amplifying characteristics of a thermionic tube are linear, except at. the two extreme ends of the grid bias voltage. Therefore, in view of the fact that the responses of the photo-electric cell are also linear, the quantity of current that flows through the plate circuit of the thermionic tube H5 is linear with respect to the amount of light falling upon the photo-electric cell IIO. Because of the linear amplifying characteristics of the thermionic tube, the current that flows through the coil of the relay 525 and the winding of the recording meter 526 is likewise directly proportional to the readings of the relative humidity.

A spring 524 having an adjustment nut is adapted to bias the armature of the relay downwardly and thus oppose the magnetic force of the coil of the relay. The circuit connections for the contacts of the relay 525 constitute a pole changer such that, when the mag eticpuil of the coil is greater than the spring bias, the armature is in the raised position and 8- current of one polarity is delivered from the supply source to the humidifying equipment; and when the magnetic pull is less than the spring bias, thearmature is in the lowered position and a current of the opposite polarity is delivered from the supply source to the humidifying equipment. When the armature of the relay is balanced, no current is delivered to the humidifyin q pment. Inasmuch as the humidifying equipment constitutes no part of my invention, I have omitted making a showing thereof. Briefly, the operation of the humidifying equipment may be such'that, when a current of one polarity is delivered thereto, the humidifying equipment responds to increase the moisture content of the surrounding air, and when no current or when a current of the opposite polarity is delivered thereto, the humidifying equipment responds to deliver nomoisture content to the surrounding air. This means that, by adjusting the tension of the spring 524, the humidifying equipment may be so regulated as to maintain the relative humidity of the surrounding air at a predetermined selected value. Also, there will be described on the paperof the recording meter 525 a graph of the relative humidity readings.

In Fig. 14, I show a modified form of a relative humidity control circuit, in which power grid-glow tubes 35I and 365 are employed to pass suflicient current to actuate a relatively large electromagnet 523 that may be mechanically connected to an operating valve 53I of the humidifying equipment. This circuit is substantially the same as the control circuit shown in Fig. 35 of my pending application .for Letters Patent, Serial No. 606,837, filed April 22, 1932, entitled, Measuring and regulating devices and like reference characters represent like parts, the only difference being that the power grid-glow tubes "I and 355 deliver current to the electroinagnet 528 instead of to the armature of the dynamo-electric machine 350 and that the amountof light falling upon the photo-electric cell 335 is determined by the relative humidity graph-member 520 of the psychrometric device instead of the graph-member lIiI of the electrical meter'394. As illustrated, a relatively strong spring 535 having an adjustment nut 529 is adapted to oppose the magnetic force of the electromagnet 528. As is apparent, this modified form of humidity control is very sensitive and, accordingly, the modulations or the variations from. a normal or predetermined selected relative humidity value is reduced to a minimum. Asillustrated,arecording meter 521 is con-' nected in series circuit relation with the electromagnet 523 and thus a graph of the relative humidity readings will be described on the recording paper thereof. Therefore, from the foregoing, it is observed that my psychrometric device provides for measuring and recording the relative humidity for any and all possible combinations of dry and wet temperature readings, as well as for so regulating and humidifying equipment of an air conditioning system that the relative humidity of the surrounding air is maintained at a predetermined selected value.

' As illustrated, the inner end of the wet bulb temperature hand 558 passes through a suitable arcuate aperture 52! in the dial or face 509 and is connected to the rim of a gear wheel 5I9, which is rotatably and freely mounted upon the tubular shaft 5I0' immediately in rear of the dial or face 509. The gear'wheel 5I3 meshes with the gear wheel 520 that is mounted on the right end of the wet bulb shaft 50I. The gear wheels 5I9 and 525 have the same diameters andpaccordingly, any angular displacement of the wet-bulb shaft 50I is directly transmitted to the wet-bulb temperature hand 508.

As hereinbefore mentioned that part of the psychrome'tric device for measuring the effective temperature is based upon the reorganized psychrometric chart of Fig. 4. In view of the by the illustrated embodiment.

fact that several ways may be employed to measure the effective temperature, as based upon the chart in Fig. 4, I do not intend to be limited In carrying out my invention, the principal object is to subtract a value (subtrahend) from the reading of the dry-bulb temperature (minuend) such that the remainder equals the effective temperature. With reference to Figs. 7 and 9, I propose to perform this subtraction by utilizing the combination of a slidably mounted collar 555 having a cam 550 mounted thereon which engages a pin 562 that is carried by a second collar 56! to which the inner end of the effective temperature hand 50! is connected. As illustrated, the inner end of the effective temperature hand 50'! passes throu h the arcuate aperture 52! in the dial or face 509 and thence through a suitably provided aperture in the web of the gear wheel |9 to the point where it is connected to the .collar 56!. As shown in Fig. 9, a part of the tubular shaft 510 is slotted where the collar 555 is keyed by means of the key 556, or other suitable means, to the dry-bulb temperature shaft 500. In this manner, the collar 555 may move axially but is constrained to move angularly with the dry-bulb temperature shaft 560. Therefore, by axially moving the slidably mounted collar 555 to the right, the cam 560 engages the pin 562 and rotates the collar 56 that carries the effective tem perature hand 50'! backwards so that the effective hand reads a value less than the dry-bulb temperature hand 505 by an amount equal to the subtrahend. In other words, the axial displacement of the collar 555 and, consequently, the backward rotation of the collar 56! corresponds to the subtrahend values, as marked off on the line 0X of 'Fig. 4. Therefore, it remains to show how the axial displacement of the collar 555 is governed by the combination of the drybulb temperature, the differential temperature, and the air velocity. To this end, I provide a slotted arm 552, in which the upper end of a pin 55! that is connected to the collar 555 is disposed to slide when the dry-bulb temperature shaft 500 is rotated between the dry-bulb temperature readings of 46? and 120. The lower end of the sl'otted arm 552 is pivotally connected at a pivot-point 570 to a slidably mounted mem her 548 that is actuated in accordance with the air velocity, and the upper end of the slotted arm 552 is actuated by a slide bar 553 that is governed in accordance with the differential temperature.

The slide bar 553 is carried by a suitable bracket 55! and the left end thereof is adapted to engage a cam 542 that is suitably mounted upon the periphery of a disc 54! which may be keyed. or otherwise connected. to the tubular shaft 5). The shape of the cam 542 is based upon the graph in Fig. 5, which represents the relationship between the linear units, as marked off on the differential temperature scale CD of Fig. 4 and the corresponding differential temperatures. Therefore, the upper end of the slottedarm 552 is actuated in accordance with the differential temperature. In the position as shown, the differential temperature is.18.

The lower end of the slotted bar 552 is actuated in accordance with the air velocity. The reference character 543 represents a shaft that is adapted to be rotated by an anemometer ('not shown). For this particular application, the anemometer may be of the vane type, wherein the position of the vane is determined by the force or velocity of the air. No showing of the anemometer is included in the drawings because it constitutes no part of my invention. The end of the anemometer shaft 543 is provided with a worm 545 which engages a worm wheel 546 that rotates'a polar cam 54!, all of which is carried by a suitable support 544. Extending outwardly at an angle equal to the angle that the line EF makes with the line OX of Fig. 4 is a bracket 55!] havingupwardly extending spaced ears in which the member 548 is slidably mounted. The lower end of the slidably mounted member 545 engages the periphery of the polar cam 541. A spring 549 disposed between the upwardly extending spaced ears and surrounding the member 548 is adapted to bias the lower end of the member 548 against the polar cam 54?. The shape of the polar cam. 54! is based upon the polar graph in Fig. 6, which represents the polar relationship between the linear units, as marked off on the line EF of Fig. 4, and the corresponding air velocities. Therefore, the slidably mounted'member 548 may be moved in and out by the rotation of the anemometer shaft 543 so that the position of the pivot-point 51!) corresponds to the air velocity values, as marked off on the line EF of Fig. 4. In the position as shown, the arm 552 may assume any one of an infinite number of positions and, at any one setting, it is analogous to one of the family of lines interconnecting the lines circumference of the disc 54! (Fig. 7), and the arcuate position of the slide rod 553 relative to the pivot-point 5'!!! is determined by the insertion of the radius line T (corresponding to 120 DB) with thearcuate line 54! (Fig. 3) or the circum ference of the disc 54! (Fig. 7). In the position, as indicated, the pivot-point 5'!!! therefore represents a dry-bulb temperature of 46 and the position of the slide rod 553 always represents a dry-bulb temperature. of 120. The pin 55'! is positioned at a dry-bulb temperature of by shaft 500 and collar 555. A so the intersection of the radius lines V (or 0 differential) and W (or 35 differential) with the arcuate line 54! (Fig. 7) or the circumference of the disc 54! determines the arcuate length of the cam 542. In the posit on as shown, the disc 54! has been rotated by the shaft 5! 0 in a clockwise direction to the point where a differential temperature of 18 on the cam 542 coincides with the engaging end of the slide rod 553. Therefore, the slidably mounted collar'555 is axially actuated to the right to such a position that the cam 560, in combination with the pin 562 and the collar 56!, retracts the effective hand 50'! an angular distance equal to 10. This means that with a dry-bulb temperature of 90, and a wet-bulb temperature of 72 (a difference of 18) the effective temperature is 80, or 10 less than the dry-bulb temperaturereading.

Depending from the collar 56! is an effective temperature graph-member 564. The light transmitting portion of the effective temperaturev graph-member 564. has an arcuate base line with effective temperaturereadings ranging from 46 to and to every value of the temperature reading there corresponds an ordinate of equal value. In the position as shown in Fig. 10,.the

plane of light is represented by the dotted line and it is passing through the' light transmitting portion at an effective temperature reading of 80. A spring 566 is connected to this graphmember in order to bias the effective hand in a clockwise direction, thus causing the pin 562 to yieldingly engage the edge of the cam 560. This causes a longitudinal force to be exerted upon the slidably mounted collar 555, with the result that the slide rod 553 is likewise yieldingly constrained against the cam 542.

As is apparent, by means of the effective temperature graph-member 564, in combination with a photo-electric cell and suitable amplifying circuit and an appropriate relay for regulating the control current delivered to the air conditioning equipment, the condition of the air in a building may be maintained at a predetermined selected effective temperature.

In theaters and department stores, which are cooled artificially in warm weather, the contrast between the outdoor and indoor air conditions, becomes the deciding factor in regard to the most desirable effective temperature to be maintained in the inside of the building. The object of cooling theaters in the summer is not to reduce the effective temperature to the optimum value, but to maintain therein a reasonably comfortable effective temperature and at the same time to avoid sensations of chill or of intense heat in entering and leaving the building. The relationship between desirable indoor effective temperature in summer corresponding to various outdoor effective temperatures is plotted in Fig. 12. The effective temperature values for the curve in Fig. 12 are listed in the chart immediately below the figure. All of these values listed in the chart, except those for the outside effective temperatures, were taken from a table appearing on page 82 of the 1931 edition of the American Society and Heating and Ventilating Engineers Guide. The values appearing in the outside effective temperature column were taken from the psychrometric chart in Fig. 1, using the corresponding outside dryand wet-bulb temperatures with the same number of grains of moisture per pound of dry air. It is noted that the effective temperature values for the curve in Fig. 12 substantially define a straight line and for all practical purposes it may be considered as such, and. that the higher the effective temperature on the outside, the higher the corresponding effective temperature on the inside. Therefore, from the foregoing, we observe that the control circuits which regulate the air conditioning equipment must be such as to respond to both the outsideand inside effective temperatures. Such a control circuit is shown in Fig. 11. In general, this control circuit comprises two independent amplifying circuits, which differentially act to operate a relay for reversing the polarity of the'current delivered from the supply source to the control apparatus of the air conditioning equipment. This means that at least two phychrometric devices must be utilized; one placed on the outside of the building and the other located on the inside of the building. The upper amplifying circuit is responsive to the outside effective temperatures and the plate current that flows through the coil 58!] is disposed to exert a force that opposes the force set up by the plate current that flows through the coil 582, which is responsive to the inside effective temperatures. The spring 585 having an adjustment nut is likewise arranged to oppose the magnetic force of the coil 582. As illustrated, an

adjustable resistor SM is connected in shunt with the coil 580, so that the magnetic force of the coil 580 is relatively weak as compared to the magnetic force of the coil 582. The relative values of the magnetic force of the coils 580 and 582, together with the spring force, are such that, for example, with an outside effective temperature of 682 and with an inside effective temperature of 67 the armature of the relay is balanced and the air conditioning equipment is inoperative. However, should the outside effective temperature rise, the balanced condition of the relay is disturbed, berause the amplifying circuit that is responsive to the outside air conditions passes more current to increase the magnetic pull ofthe coil 580. This causes the air conditioning equipment to respond until the inside effective temperature is raised to a point where the armature of the relay again becomes balanced. In other words a change in the outside effective temperature causes such a change in the inside effective temperature that the relationship conforms substantially with the curve shown in Fig. 12, or with any other desirable relationship which gives the most comfortable feelmg.

As illustrated, a recording meter 583 and a recording meter 584 may be employed to record the outside and inside effective temperature readings, respectively.

In Fig. 15, I show a fragmentary view of a modified form of the effective temperature control circuits, in which two power grid-glow tube circuits, such as the one illustrated in Fig. 14, may be employed to operate a valve 592, or other control means of the air conditioning equipment, by means of two electro-magnets 590 and BM directly connected thereto, which are energized by the power grid-glow tubes. Also two recording meters 593 and 594 may be utilized to record, respectively, the outside and inside effective temperatures.

As shown in Fig. 15, the valve 592 may, for example, control the flow of a heating medium in a pipe 602 leading to a conventional radiator (not shown) Hot water or steam may be supplied to the valve from a heating plant 600 provided with the usual riser pipe 60! and return pipe 603.

In Fig. 16 I have shown a conventional conditioning apparatus which may be controlled by means of a control system of the type shown in Fig. 11. Reference numeral 810 designates a conventional heating plant which is adapted to supply a heating medium such as steam or hot water to the usual form of radiator 6l5. A solenoid valve H4 is shown in the riser pipe M3 for controlling the flow of the heating medium through the radiator 6|5. H4 is controlled by a magnetically operated switch of the type shown in Fig. 11.

Inasmuch as the effective temperature is a measure of any and all possible combinations of the dry-bulb temperature, the relative humidity, and the air velocity, the effective temperature control circuits of Figs. 11 and 15 may regulate any one of the three factors while the other two may be allowed to vary uncontrolled. For example, if the control circuits of Figs. 11 and15 are arranged to regulate the dry-bulb temperature only, the relative humidity and the air velocity may vary uncontrolled, because the drybulb temperature remains at the same predetermined selected value. In other words, my effective temperature control system is such that,

The solenoid valve for any change in the relative humidity or the air velocity which results in a change in the effective temperature, the dry-bulb temperature is corrected to off-set the said change in the effective temperature caused by the change in the relative humidity and the air velocity. Therefore, even though the relative humidity and the air velocity may vary uncontrolled, the efiective temperature is maintained at a predetermined selected value. In those cases where the air velocity is held constant, it is not necessary to use an anemometer, but the position of the slidably mounted member 548 may be adjustably set, by a set screw or other suitable means, at values that correspond to the predetermined selected constant air velocity.

It is to be pointed out that the amplifying circuits used through my invention are merely illustrative and, accordingly, they may take other forms. In the illustrated forms, the constancy or calibration of the circuits remain very accurate over a reasonable length of time, which is usually at least a year or more and this condition will improve with the manufacture of better tubes. However, should the operating conditions require that no change in the calibration take place over a period of several years, a null method may be employed, which counterbalances comprising, in combination, means influenced by the dry-bulb temperature, means influenced by the wet-bulb temperature, means governed by the two foregoing means for giving a resultant movement that is a measurement of the efiective temperature, in combination of moisture and temperature, the arrangement of the drybulb temperature means and the wet-bulb temperature 'means being such that the value of the effective temperature lies between the value of the dry-bulb temperature and the wet-bulb temperature, an air conditioner, circuit connections for controlling the air conditioner, a lightsensitive device associated with the circuit connections, a light source for affecting the light sensitive device, and means governed by the resultant movement for controlling the amount of light falling upon the light sensitive device.

2. A device for regulating the effective temperature in combinations of moisture and temperature, and the relative humidity comprising, in combination, means influenced by the drybulb temperature, means influenced by the wetbulb temperature, differential means governed by the dry-bulb temperature and the wet-bulb temperature, two separate means respectively governed by the dry-bulb temperature and the diiferential means, one of said separate means being adapted to give the measurement of the efiective temperature in combinations of moisture and temperature, and the other separate means being adapted to give the measurement of the relative humidity, circuit connections for controlling an air conditioner and a humiditying device that afiect the .conditlon of the-:air

so as to maintain a predetermined effective tem perature, means responsive to one of the separate meansfor controlling the circuit connections that regulate the air conditioner, and means responsive to the other separate means for controlling the circuit connections that regulate the humidifying device.

3. A device for regulating a device that affects the condition of the air comprising, in combination, means for giving a measurement of the dry-bulb temperature, means responsive to the dry-bulb temperature and the moisture for giving a subtrahend value, means for subtracting the subtrahend value from the measurement of the dry-bulb temperature to give a modified measurement, circuit connections for controlling a device that affects the condition of the air, and means responsive to the modified measurement for controlling the circuit connections.

4. The improvement in the art of air conditioning where the moisture varies uncontrolled and where the temperature is controlled to maintain a substantially constant condition of the air in combinations of moisture and temperature which comprises automatically controlling the condition of the air to provide a higher or lower dry-bulb temperature as the relative humidity respectively decreases or increases, and automatically regulating the efiect of said control so as to give a greater temperature correction with respect to a unit change of relative humidity as the value of the dry-bulb temperais greater at higher temperatures than at lower temperatures and that the value of the said measurement lies between the value of the drybulb temperature and the wet-bulb temperature, an air conditioner, circuit connections for controlling the air conditioner, and means responsive to the said measurement for controlling the circuit connections.

6. In combination, a plurality of means responsive to functions of the psychrometric conditions of air, control means actuated by the joint action of said first means, a member movable in response to air motion for modifying the action of one of said means, and means for varying the psychrometric condition of air responsive to said control means.

7. The combination with means for varying the dry-bulb temperature, of a regulating device that is responsive to the combination of the drybulb temperature and the relative humidity, the arrangement of the regulating device being such that the rate at which the moisture influences the action of the regulating device is greater at higher temperatures than at lower temperatures, and control circuits inter-connecting the drybulb temperature varying means and the regulating devicefor so regulating the dry-bulb temperature varying means that, for any unit change in the relative humidity at difierent dry-bulb temperatures, the dry-bulb temperature is corrected a variable amount to off-set the change in the condition of the air caused by the change in the relative humidity.

8. The combination with means for varying the dry-bulb temperature, of a regulating device having means influenced by the dry-bulb temperature and by the moisture and having a regulating member receiving motion from each of said dry-bulb temperature means and said moisture means and resolving said motion into a resultant movement of its own for regulating the dry-bulb temperature varying means, the arrangement of the dry-bulb temperature means, the moisture means and the regulating member of the regulating device being such that the rate at which the moisture influences the movement of the regulating member is greater at higher temperatures than at lower temperatures, and means governed by the movements of the regulating member for so regulating the dry-bulb temperature varying means that, for any change in the relative humidity, the dry-bulb temperature is corrected a greater amount at higher temperatures than at lower temperatures to oilset the change in the condition of the air caused by the said change in the relative humidity.

9. The combination with means for varying the dry-bulb temperature, of a regulating device having means influenced by the dry-bulb temperature and by the moisture and having a regulating member receiving motion from each of said dry-bulb temperature means and said moisture means and resolving said motion into a resultant movement of its own for regulating the dry-bulb temperature varying means, the arrangement of the dry-bulb temperature means, the moisture means and the regulating member of the regulating device being such that the rate at which the moisture influences the movement of the regulating member is greater at higher temperatures than at lower temperatures, cir- .cuit connections for controlling the dry-bulb 

